Noble-Metal-Free Copper Nanoparticles/Reduced Graphene Oxide Composite: A New and Highly Efficient Catalyst for Transformation of 4-Nitrophenol

Carbon-Dots-Initiated Photopolymerization: An In Situ Synthetic Approach for MXene/Poly(norepinephrine)/Copper Hybrid and its Application for Mitigating Water Pollution

The current work presents a facile and green synthesis of carbon quantum dots (C-dots), which could serve as initiators for polymerization. Herein, C-dots have been synthesized from an easily available green herb, dill leaves, by a single-step hydrothermal method. These C-dots were efficiently utilized as initiators for the photopolymerization of the polymer poly(norepinephrine) (PNE) for the first time. The photopolymerization is discussed by a factorial design, and the optimized synthesis conditions were evaluated by a third-order regression model of three reaction parameters: monomer concentration, C-dots concentration, and UV exposure time. The sign convention of the factorial design mode indicated that monomer concentration and time of exposure are the most important factors for polymerization. The photopolymerized poly(norepinephrine) was extensively studied using Fourier transform infrared (FTIR) analysis, X-ray photoelectron spectroscopy (XPS), mass spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle measurement, and thermogravimetric analysis (TGA). UV-assisted deposition of PNE on six different types of substrates was performed, and their water contact angle and surface morphology were studied to evaluate the coating. This UV-triggered polymerization technique was further applied to fabricate sandwich-like composite catalyst MXene/poly(norepinephrine)/copper nanoparticles. This catalyst displayed good performance in the reduction of 4-NP (4-nitrophenol) at ambient temperature, and the first-order rate constant of the catalysis was 9.39 × 10^-3 s^-1. The reusability of the catalyst was evaluated in terms of the conversion factor. After 10 catalytic cycles, the conversion to catalyze 4-NP was still greater than 91%. The catalytic performance was also evaluated in the continuous flow condition through a membrane, fabricated from a cellulose filter paper coated with MXene/poly(norepinephrine)/copper nanoparticles. This composite catalyst not only offers a practical mode for the catalytic reaction of MXene-based materials but also lays down the foundation for the development of new catalysts.

Electrochemical Deposition of Copper on Epitaxial Graphene

Understanding the mechanism of metal electrodeposition on graphene as the simplest building block of all graphitic materials is important for electrocatalysis and the creation of metal contacts in electronics. The present work investigates copper electrodeposition onto epitaxial graphene on 4H-SiC by experimental and computational techniques. The two subsequent single-electron transfer steps were coherently quantified by electrochemistry and density functional theory (DFT). The kinetic measurements revealed the instantaneous nucleation mechanism of copper (Cu) electrodeposition, controlled by the convergent diffusion of reactant to the limited number of nucleation sites. Cu can freely migrate across the electrode surface. These findings provide fundamental insights into the nature of copper reduction and nucleation mechanisms and can be used as a starting point for performing more sophisticated investigations and developing real applications.

Highly efficient and stable catalysis of p-nitrophenol via silver/lignin/polyacrylic acid hydrogel

As the second largest natural polymer in nature, lignin has a large amount of reserves and has important practical application value, which has attracted increasing attention. Ag@LPAH, a nanometer silver catalyst with a 3D structure, was successfully prepared in a simple operation. In batch experiment and fixed-bed experiment, it showed excellent catalytic degradation ability and stability of 4-NP. Thanks to the large number of carboxyl groups present in the lignin-polyacrylic acid hydrogel, the silver nanoparticles are well controlled to grow with no agglomeration. Ag@LPAH-20 exhibited optimal catalytic performance and stability, requiring only 123 s to complete the reaction and maintaining 99% catalytic efficiency after 10 cycles. In addition, the catalytic efficiency can be maintained over 90% for more than 120 min in fixed bed experiment.

Enhanced catalytic activity of nanosilver with lignin/polyacrylamide hydrogel for reducing p-nitrophenol

Lignin, as the second largest natural polymer in nature, has great practical application value. Three-dimensional silver/lignin/PAM hydrogels have been successfully prepared via a rapid and convenient assembly process, showing good catalytic hydrogenation ability and stability in batch and dynamic catalytic processes of p-nitrophenol. It can be seen from the characterization results that abundant amino groups in the catalyst carrier can disperse silver ions homogeneously and limit the growth of silver nanoparticles in the reduction process with sodium borohydride. At room temperature, the catalytic process can be completed in about 5 min by using this catalyst and can maintain about 100 min of efficient catalysis in the dynamic catalytic experiment, the conversion rate can reach about 80%. After 10 times use, the catalyst still maintained good catalytic performance and the conversion rate could be kept at 97%.

Highly recyclable Ag NPs/alginate composite beads prepared via one-pot encapsulation method for efficient continuous reduction of p-nitrophenol

Recyclable Ag NPs/alginate composite beads, performing well in dynamic catalytic hydrogenation of p-nitrophenol, were prepared via a one-pot encapsulation method.